EP0176121B1 - Method for detecting and eliminating parasitic pictures produced by a pyramidal ir dome - Google Patents

Method for detecting and eliminating parasitic pictures produced by a pyramidal ir dome Download PDF

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Publication number
EP0176121B1
EP0176121B1 EP85201327A EP85201327A EP0176121B1 EP 0176121 B1 EP0176121 B1 EP 0176121B1 EP 85201327 A EP85201327 A EP 85201327A EP 85201327 A EP85201327 A EP 85201327A EP 0176121 B1 EP0176121 B1 EP 0176121B1
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European Patent Office
Prior art keywords
image
frame
dome
parasitic
comparator
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German (de)
French (fr)
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EP0176121A1 (en
Inventor
Pierre Marche
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Cessione thomson - Trt Defense
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Telecommunications Radioelectriques et Telephoniques SA TRT
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/42—Housings not intimately mechanically associated with radiating elements, e.g. radome
    • H01Q1/421—Means for correcting aberrations introduced by a radome
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41G—WEAPON SIGHTS; AIMING
    • F41G7/00—Direction control systems for self-propelled missiles
    • F41G7/20—Direction control systems for self-propelled missiles based on continuous observation of target position
    • F41G7/22—Homing guidance systems
    • F41G7/2253—Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41G—WEAPON SIGHTS; AIMING
    • F41G7/00—Direction control systems for self-propelled missiles
    • F41G7/20—Direction control systems for self-propelled missiles based on continuous observation of target position
    • F41G7/22—Homing guidance systems
    • F41G7/2273—Homing guidance systems characterised by the type of waves
    • F41G7/2293—Homing guidance systems characterised by the type of waves using electromagnetic waves other than radio waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/78—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using electromagnetic waves other than radio waves
    • G01S3/782—Systems for determining direction or deviation from predetermined direction
    • G01S3/785—Systems for determining direction or deviation from predetermined direction using adjustment of orientation of directivity characteristics of a detector or detector system to give a desired condition of signal derived from that detector or detector system
    • G01S3/786—Systems for determining direction or deviation from predetermined direction using adjustment of orientation of directivity characteristics of a detector or detector system to give a desired condition of signal derived from that detector or detector system the desired condition being maintained automatically

Definitions

  • the invention relates to a method for detecting and eliminating parasitic images created by the infrared pyramid dome of an infrared seeker for a missile not stabilized in roll.
  • the analysis of the scene located in the field of the objective concerns sources such as for example the useful target, an element of the landscape, a lure, etc ... (origin of the first type).
  • the analysis of the scene located outside the scope of the objective relates to sources such as for example an element of the landscape (including the sun), a decoy, etc. (origin of the second type).
  • the images that we propose to eliminate here are those corresponding to an origin of the second type, whether they are landscape elements or decoys, the distinction between landscape elements and decoys, not being operated.
  • the method according to the invention is remarkable in that it comprises the formation of an image of a scene delimited by the field of the objective of the seeker in the focal plane of said objective after transmission through the dome and the analysis of said image with a raster scan of period T whose value is different from a multiple of the trajectory period defined as the ratio of the period of rotation of the missile's roll to the number of facets of said dome, said scan being obtained by analyzing the image in said focal plane of the lens by means of a strip of infrared detectors, the image of said scene formed on the strip comprising, superimposed on the useful part corresponding to said scene delimited by the seeker field, a spurious image corresponding to a scene located outside of said field and the flux transmitted through one of the facets of the dome is reflected on the external face of an opposite facet, the a method further comprising storing the electrical signals from said detectors in a frame memory, the signal levels corresponding to points of the frame of rank N-1 preceding any frame of rank N being stored in said memory, the transmission of
  • this process is intended for a missile not stabilized in roll. It is therefore an aid for flight hooking, flight re-hanging and pursuit.
  • the elementary duration of the treatment is limited to a sufficiently low value (for example a frame period of 5 ms) such that it is possible to neglect in particular the displacement of the missile (3.5 m at Mach 2), the displacement relative target-missile, the magnification of the target (less than an elementary field of 0.5 m rd for a target of diameter 2 m at the very short distance of 100 m), the images of the first type remain identical, while the images of the second type describe a trajectory during the same time.
  • a sufficiently low value for example a frame period of 5 ms
  • FIG. 1 representing the cross section of an IR pyramid dome 1 by its plane of symmetry shows that the transmitted radiation can have two origins:
  • a complete analysis of the scene delimits the field of the seeker according to its characteristics (optical system, detectors, scanning mode).
  • the image thus obtained in the focal plane of the objective constitutes a frame represented in FIG. 2.
  • the infrared detectors 8 are arranged in a strip B of 32 elements.
  • An unrepresented prism rotating at the objective produces the rotation of the image in the scene plane.
  • Each detector element therefore analyzes a circular crown centered in Co.
  • the flux which it receives is integrated and read sequentially for a certain time according to the speed of rotation every 1/128 turn.
  • One of these elements is represented around the point M of polar coordinates p and ⁇ p. If the scanning speed is 200 t / s, the frame period is 5 ms.
  • the levels of the signals corresponding to the various picture elements on the successive frames are transmitted to the inputs of a differential detector 11, by direct route on the non-inverting input and through a memory 10 on the inverting input.
  • the memory 10 known as frame memory is equivalent to a delay line of length equal to the duration of a frame period T.
  • the comparator output provides a logic signal L.
  • Also defined in FIG. 4a is the reflection facet as well as the directions of the incident and reflected rays.
  • the facet plane of reflection is defined by two lines: the axis y'Oy and the line Ow, intersection of the plane xOz with a plane parallel to the facet of the IR dome on which the radiation coming from the spurious source is reflected.
  • the line Ow makes an angle 8 with the axis x'Ox.
  • the direction of the incident beam is given by the straight line OS which makes an angle ⁇ with the facet in the plane xOz.
  • Figure 4b shows the above definitions in the xOz plane at the initial time.
  • the center O of fixed reference frame Oxyz is positioned at the center of the optical system of the seeker.
  • this optical system is represented in a simplified manner by a lens 11 located in the body of the missile 14 adjoining the IR pyramid dome 1.
  • y be the angle of sight, that is to say the movement of the seeker head or in the simplified representation of the figure, the angle of the optical axis of the lens 11 with the x'Ox axis of the missile.
  • the vector C o R has as components:
  • the focal plane is defined as the plane perpendicular to the line of sight shown in Figure 7 and given by its site ⁇ (counted positively upwards) and its azimuth e (counted counterclockwise in the horizontal plane) and such that the point C o (center of the field) is at the distance F from the origin 0.
  • the vector C o R has as components:

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Closed-Circuit Television Systems (AREA)
  • Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)

Description

L'invention concerne un procédé de détection et d'élimination d'images parasites créées par le dôme pyramidal à infrarouge d'un autodirecteur infrarouge pour missile non stabilisé en roulis.The invention relates to a method for detecting and eliminating parasitic images created by the infrared pyramid dome of an infrared seeker for a missile not stabilized in roll.

L'analyse de la scène située dans le champ de l'objectif concerne des sources telles que par exemple la cible utile, un élément du paysage, un leurre, etc... (origine du premier type).The analysis of the scene located in the field of the objective concerns sources such as for example the useful target, an element of the landscape, a lure, etc ... (origin of the first type).

L'analyse de la scène située en dehors du champ de l'objectif concerne des sources telles que par exemple un élément .du paysage (dont le soleil), un leurre, etc... (origine du deuxième type).The analysis of the scene located outside the scope of the objective relates to sources such as for example an element of the landscape (including the sun), a decoy, etc. (origin of the second type).

Les images que l'on se propose ici d'éliminer sont celles correspondant à une origine du deuxiène type, qu'il s'agisse d'éléments du paysage ou de leurres, la distinction entre éléments de paysages et leurres, n'étant pas opérée.The images that we propose to eliminate here are those corresponding to an origin of the second type, whether they are landscape elements or decoys, the distinction between landscape elements and decoys, not being operated.

Le remède théorique à la non-création de telles images parasites consiste à effectuer sur la face externe de chaque facette de l'IR dôme un traitement anti-reflet analogue à celui qui est opéré sur les faces internes. Ce remède s'avère pratiquement inefficace du fait que les traitements connus à ce jour ne résistent pas aux contraintes d'environnement subies par l'IR dôme.The theoretical remedy for the non-creation of such parasitic images consists in carrying out on the external face of each facet of the IR dome an anti-reflection treatment similar to that which is operated on the internal faces. This remedy turns out to be practically ineffective because the treatments known to date do not withstand the environmental constraints suffered by the IR dome.

On connaît par ailleurs du brevet anglais 2 071 957, un dispositif électronique de détection et d'élimination d'images parasites dont le principe peut être appliqué à l'élimination des images parasites introduites par l'IR dôme pyramidal d'un autodirecteur de missile selon le procédé de l'invention.Also known from English patent 2,071,957 is an electronic device for detecting and eliminating spurious images, the principle of which can be applied to the elimination of spurious images introduced by the IR pyramid dome of a missile seeker. according to the method of the invention.

Le procédé selon l'invention est remarquable en ce qu'il comporte la formation d'une image d'une scène délimitée par le champ de l'objectif de l'autodirecteur dans le plan focal dudit objectif après transmission à travers le dôme et l'analyse de ladite image avec un balayage-trame de période T dont la valeur est différente d'un multiple de la période de trajectoire définie comme le rapport de la période de rotation en roulis du missile au nombre de facettes dudit dôme, ledit balayage étant obtenu par l'analyse de l'image dans ledit plan focal de l'objectif au moyen d'une barrette de détecteurs infrarouges, l'image de ladite scène formée sur la barrette comportant, superposée à la partie utile correspondant à ladite scène délimitée par le champ de l'autodirecteur, une image parasite correspondant à une scène située en dehors dudit champ et dont le flux transmis à travers l'une des facettes du dôme est réfléchi sur la face externe d'une facette opposée, le procédé comportant en outre la mémorisation des signaux électriques issus desdits détecteurs dans une mémoire de trame, les niveaux des signaux correspondant à des points de la trame de rang N-1 précédant une trame quelconque de rang N étant stockés dans ladite mémoire, la transmission des niveaux des signaux correspondant à deux points d'une même localisation géographique de la scène, l'un sur la trame de rang N à un instant t, l'autre sur la trame de rang N-1 à l'instant t-T, respectivement à l'entrée non .inverseuse et à l'entrée inverseuse d'un détecteur différentiel dont la sortie est reliée à travers un opérateur de prise de valeur absolue à une première entrée d'un comparateur, la comparaison du signal présent sur ladite première entrée du comparateur à une tension de seuil de valeur positive appliquée à la seconde entrée dudit comparateur, le signal issu dudit opérateur indiquant l'apparition d'une image parasite si sa valeur est supérieure à ladite valeur de seuil, l'inhibition de la prise en compte de ladite image parasite par le signal de sortie dudit comparateur.The method according to the invention is remarkable in that it comprises the formation of an image of a scene delimited by the field of the objective of the seeker in the focal plane of said objective after transmission through the dome and the analysis of said image with a raster scan of period T whose value is different from a multiple of the trajectory period defined as the ratio of the period of rotation of the missile's roll to the number of facets of said dome, said scan being obtained by analyzing the image in said focal plane of the lens by means of a strip of infrared detectors, the image of said scene formed on the strip comprising, superimposed on the useful part corresponding to said scene delimited by the seeker field, a spurious image corresponding to a scene located outside of said field and the flux transmitted through one of the facets of the dome is reflected on the external face of an opposite facet, the a method further comprising storing the electrical signals from said detectors in a frame memory, the signal levels corresponding to points of the frame of rank N-1 preceding any frame of rank N being stored in said memory, the transmission of signal levels corresponding to two points of the same geographic location of the scene, one on the frame of rank N at an instant t, the other on the frame of rank N-1 at time tT, respectively at the non-inverting input and the inverting input of a differential detector whose output is connected through an operator for taking an absolute value to a first input of a comparator, the comparison of the signal present on said first input of the comparator at a positive value threshold voltage applied to the second input of said comparator, the signal from said operator indicating the appearance of a spurious image if its value is greater re at said threshold value, the inhibition of taking into account of said parasitic image by the output signal of said comparator.

Comme il a déjà été mentionné dans le préambule, ce procédé s'adresse à un missile non stabilisé en roulis. Il s'agit donc d'une aide à l'accrochage en vol, au réaccrochage en vol et à la poursuite.As already mentioned in the preamble, this process is intended for a missile not stabilized in roll. It is therefore an aid for flight hooking, flight re-hanging and pursuit.

A condition de limiter la durée élémentaire du traitement à une valeur suffisamment faible (par exemple une période de trame de 5 ms) telle qu'il soit possible de négliger notamment le déplacement du missile (3,5 m à Mach 2), le déplacement relatif cible-missile, le grossissement de la cible (inférieur à un champ élémentaire de 0, 5 m rd pour une cible de diamètre 2 m à la très courte distance de 100 m), les images du premier type restent identiques, alors que les images du deuxième type décrivent une trajectoire pendant le même temps.On condition that the elementary duration of the treatment is limited to a sufficiently low value (for example a frame period of 5 ms) such that it is possible to neglect in particular the displacement of the missile (3.5 m at Mach 2), the displacement relative target-missile, the magnification of the target (less than an elementary field of 0.5 m rd for a target of diameter 2 m at the very short distance of 100 m), the images of the first type remain identical, while the images of the second type describe a trajectory during the same time.

La description suivante en regard des dessins annexés, le tout donné à titre d'exemple fera bien comprendre comment l'invention peut être réalisée.The following description with reference to the appended drawings, all given by way of example will make it clear how the invention can be implemented.

Les valeurs numériques utilisées ci-après sont données à titre indicatif et proviennent d'ordres de grandeur correspondant à une application de ce dispositif à un ADIR à imagerie pour missile sol-air à très courte portée.

  • La figure 1 représente le schéma de principe du dispositif pour la mise en oeuvre du procédé de l'invention.
  • La figure 2 représente une trame dans le plan focal de l'objectif.
  • La figure 3 représente le schéma synoptique du dispositif électronique de détection et d'élimination d'images parasites.
  • La figure 4a définit le référentiel fixe Oxyz et la facette de réflexion pour la détermination des points génériques de l'image parasite. La figure 4b donne les mêmes définitions dans le plan xOz à l'instant initial.
  • La figure 5 montre à l'intérieur du missile le positionnement du référentiel fixe par rapport au plan focal de l'objectif.
  • La figure 6 montre la trajectoire d'une image parasite dans les limites du champ analysé.
  • La figure 7 définit le référentiel fixe et l'axe de visée dans le cas général où aucune hypothèse n'est faite sur l'existence de l'image parasite à t = 0.
The numerical values used below are given as an indication and come from orders of magnitude corresponding to an application of this device to an ADIR with imagery for very short range surface-to-air missile.
  • Figure 1 shows the block diagram of the device for implementing the method of the invention.
  • Figure 2 shows a frame in the focal plane of the lens.
  • FIG. 3 represents the block diagram of the electronic device for detecting and eliminating parasitic images.
  • FIG. 4a defines the fixed reference frame Oxyz and the reflection facet for determining the generic points of the parasitic image. Figure 4b gives the same definitions in the xOz plane at the initial time.
  • FIG. 5 shows inside the missile the positioning of the fixed reference frame with respect to the focal plane of the objective.
  • FIG. 6 shows the trajectory of a spurious image within the limits of the field analyzed.
  • Figure 7 defines the fixed frame of reference and the line of sight in the general case where no assumption is made on the existence of the stray image at t = 0.

Les éléments correspondants sur ces différentes figures seront désignés par les mêmes signes de référence.The corresponding elements in these different figures will be designated by the same reference signs.

La figuré 1 représentant la coupe d'un IR dôme pyramidal 1 par son plan de symétrie montre que le rayonnement transmis peut avoir deux origines :FIG. 1 representing the cross section of an IR pyramid dome 1 by its plane of symmetry shows that the transmitted radiation can have two origins:

une origine dite du premier type, indiquée en pointillés 2 sur la figure, lorsqu'il provient d'une source située dans le champ de l'objectif et dont le signal est recueilli dans le plan focal dudit objectif après transmission à travers l'IR dôme ;an origin known as the first type, indicated by dotted line 2 in the figure, when it comes from a source located in the field of the objective and whose signal is collected in the focal plane of said objective after transmission through the IR dome;

une origine dite du deuxième type, indiquée en trait plein 3, lorsqu'il est issu d'une source extérieure au champ de l'objectif mais dont le flux transmis à travers l'une des facettes 4 de l'IR dôme est ensuite réfléchi par la face externe 5 d'une facette opposée 6. Ce rayonnement produit dans le plan focal d'un objectif 7 une image parasite qui se superpose à l'image utile formée sur un détecteur 8 qui traduit le flux qu'il reçoit en un signal électrique. Conformément à l'invention, ce signal est introduit dans un dispositif électronique de détection et d'élimination d'images parasites 9.an origin known as of the second type, indicated in solid line 3, when it comes from a source external to the field of the objective but whose flux transmitted through one of the facets 4 of the IR dome is then reflected by the external face 5 of an opposite facet 6. This radiation produces in the focal plane of a lens 7 a parasitic image which is superimposed on the useful image formed on a detector 8 which translates the flux which it receives into a electrical signal. According to the invention, this signal is introduced into an electronic device for detecting and eliminating parasitic images 9.

Une analyse complète de la scène délimite le champ de l'autodirecteur selon ses caractéristiques (système optique, détecteurs, mode de balayage). L'image ainsi obtenue dans le plan focal de l'objectif constitue une trame representée sur la figure 2. Les détecteurs infrarouge 8 sont disposés en une barrette B de 32 éléments. Un prisme non représenté tournant au niveau de l'objectif produit la rotation de l'image dans le plan de la scène. Chaque élément détecteur analyse donc une couronne circulaire centrée en Co. Le flux qu'il reçoit est intégré et lu séquentiellement pendant un certain temps selon la vitesse de rotation tous les 1/128 tour. La trame ainsi décomposée en 128 positions successives de la barrette de détecteurs elle-même découpée géographiquement en 32 éléments est formée de 128 fois 32 = 4096 éléments d'image ou pixels (contraction des mots anglais picture elements). L'un de ces éléments est représenté autour du point M de coordonnées polaires p et <p. Si. la vitesse du balayage est de 200 t/s, la période de la trame est de 5 ms.A complete analysis of the scene delimits the field of the seeker according to its characteristics (optical system, detectors, scanning mode). The image thus obtained in the focal plane of the objective constitutes a frame represented in FIG. 2. The infrared detectors 8 are arranged in a strip B of 32 elements. An unrepresented prism rotating at the objective produces the rotation of the image in the scene plane. Each detector element therefore analyzes a circular crown centered in Co. The flux which it receives is integrated and read sequentially for a certain time according to the speed of rotation every 1/128 turn. The frame thus broken down into 128 successive positions of the array of detectors itself cut geographically into 32 elements is formed 128 times 32 = 4096 picture elements or pixels (contraction of the English words picture elements). One of these elements is represented around the point M of polar coordinates p and <p. If the scanning speed is 200 t / s, the frame period is 5 ms.

La suppression des images parasites est obtenue au moyen du dispositif électronique 9 dont le schéma synoptique est représenté sur la figure 3.The suppression of spurious images is obtained by means of the electronic device 9, the block diagram of which is shown in FIG. 3.

Les niveaux des signaux correspondant aux différents éléments d'image sur les trames successives sont transmis aux entrées d'un détecteur différentiel 11, par voie directe sur l'entrée non-inverseuse et à travers une mémoire 10 sur l'entrée inverseuse. La mémoire 10 dite mémoire de trame est équivalente à une ligne à retard de longueur égale à la durée d'une période de trame T. La sortie du détecteur différentiel 11 est reliée à travers un opérateur de prise de valeur absolue 12 à une entrée d'un comparateur 13 dont l'autre entrée reçoit une valeur de seuil So positive et fonction du niveau de bruit lhermique du dispositif (So = aσ ; a>0 ; α étant l'écart type du bruit). La sortie du comparateur fournit un signal logique L.The levels of the signals corresponding to the various picture elements on the successive frames are transmitted to the inputs of a differential detector 11, by direct route on the non-inverting input and through a memory 10 on the inverting input. The memory 10 known as frame memory is equivalent to a delay line of length equal to the duration of a frame period T. The output of the differential detector 11 is connected through an operator for taking an absolute value 12 to an input d a comparator 13, the other input of which receives a positive threshold value S o and a function of the thermal noise level of the device (S o = aσ; a>0; α being the standard deviation of the noise). The comparator output provides a logic signal L.

Le traitement est effectué en temps réel. La trame n° N étant analysée et les niveaux des points de la trame précédente n° N - 1 ayant été stockés dans la mémoire de trame 10, le détecteur différentiel 11 effectue la différence point à point entre les niveaux fournis par les trames N et N - 1. Si le point M analysé à l'instant t sur la trame N fournit le niveau S(t), le niveau du même point mis en mémoire était S(t - T) sur la trame N - 1. On calcule donc à l'instant t : AS(t) = S(t) - S(t - T) et la valeur absolue de AS(t) en provenance de 12 est comparée en 13 à la valeur de seuil So. Si l'on a |ΔS(t) ≥ So, il y a au point M variation de signal entre la trame N - 1 et la trame N, ce qui indique l'apparition d'une image parasite. Le signal logique L = 1 issu de cette comparaison va servir à inhiber la prise en compte de cette information.Processing takes place in real time. The frame n ° N being analyzed and the levels of the points of the previous frame n ° N - 1 having been stored in the frame memory 10, the differential detector 11 performs the point-to-point difference between the levels provided by the frames N and N - 1. If the point M analyzed at time t on the frame N provides the level S (t), the level of the same point stored in memory was S (t - T) on the frame N - 1. We calculate therefore at time t: AS (t) = S (t) - S (t - T) and the absolute value of AS (t) coming from 12 is compared in 13 to the threshold value S o . If we have | ΔS (t) ≥ S o , at point M there is a signal variation between frame N - 1 and frame N, which indicates the appearance of a spurious image. The logic signal L = 1 from this comparison will be used to inhibit the taking into account of this information.

La condition selon laquelle toute évolution entre deux trames consécutives (avec une période trame de faible valeur) caractérise une image parasite (origine du deuxième type) est une condition suffisante. Cela peut ne pas être une condition nécessaire.The condition that any change between two consecutive frames (with a low value frame period) characterizes a spurious image (origin of the second type) is a sufficient condition. This may not be a necessary condition.

En effet, compte tenu de la périodicité de la rotation en roulis d'une part, de la périodicité de l'analyse trame d'autre part, une image parasite peut présenter la même trajectoire lors de deux trames consécutives.Indeed, taking into account the periodicity of the roll rotation on the one hand, the periodicity of the frame analysis on the other hand, a spurious image can have the same trajectory during two consecutive frames.

Ce phénomène est rencontré lorsque la période d'analyse est un multiple de la » période trajectoire », ce qui se traduit par:

Figure imgb0001

  • avec T : période d'analyse ou durée trame
  • nf : nombre de facettes de l'IR dôme
  • w : vitesse de roulis
  • k : entier lié à la trame N.
This phenomenon is encountered when the analysis period is a multiple of the “trajectory period”, which results in:
Figure imgb0001
  • with T: analysis period or frame duration
  • n f : number of facets of the IR dome
  • w: roll speed
  • k: integer linked to frame N.

Pour l'application numérique suivante :For the following digital application:

T = 5 ms ; nf = S; 5 ≤ ω≤ 15 tours/s, ce qui fournit 0,2 ≤ k ≤ 0,6, on vérifie qu'il n'existe pas de valeur entière de k satisfaisant l'équation [E1]. Donc le phénomène précité ne risque pas de se produire.T = 5 ms; n f = S; 5 ≤ ω≤ 15 turns / s, which gives 0.2 ≤ k ≤ 0.6, we check that there is no integer value of k satisfying the equation [E1]. Therefore the aforementioned phenomenon is not likely to occur.

La durée élémentaire du traitement étant limitée à une valeur faible de l'ordre de la période trame, on a indiqué ci-dessus que les images du second type décrivent une trajectoire dont on se propose de calculer les expressions. A cet effet, on supposera que la trame est stabilisée en roulis, c'est-à-dire que les informations de luminances sont adressées dans un référentiel fixe lié au sol. Sur le plan pratique, cela résulte de l'utilisation d'un gyroscope de roulis et de la compensation électronique de l'adressage effectué dans un repère lié au missile. Le choix de l'orientation des axes est alors plus important que celui de l'origine qui peut être arbitraire. La figure 4a donne la définition de ce référentiel représenté en perspective:

  • L'axe x'Ox est l'axe du missile (Ox étant dirigé vers l'avant).
  • L'axe z'Oz est l'axe vertical du missile à t = 0 (Oz étant dirigé vers le haut).
  • L'axe y'Oy est le troisième axe de coordonnées du référentiel, Oxyz étant fixe dans l'espace (stabilisé en roulis).
The elementary duration of the processing being limited to a low value of the order of the frame period, it was indicated above that the images of the second type describe a trajectory for which it is proposed to calculate the expressions. To this end, it will be assumed that the frame is stabilized in roll, that is to say that the luminance information is addressed in a fixed reference frame linked to the ground. In practical terms, this results from the use of a roll gyroscope and electronic addressing compensation carried out in a reference linked to the missile. The choice of the orientation of the axes is then more important than that of the origin which can be arbitrary. Figure 4a gives the definition of this repository represented in perspective:
  • The x'Ox axis is the missile axis (Ox being directed forward).
  • The axis z'Oz is the vertical axis of the missile at t = 0 (Oz being directed upwards).
  • The y'Oy axis is the third coordinate axis of the frame of reference, Oxyz being fixed in space (stabilized in roll).

On définit également sur la figure 4a la facette de réflexion ainsi que les directions des rayons incident et réfléchi.Also defined in FIG. 4a is the reflection facet as well as the directions of the incident and reflected rays.

A l'instant initial, le plan facette de réflexion est défini par deux droites : l'axe y'Oy et la droite Ow, intersection du plan xOz avec un plan parallèle à la facette de l'IR dôme sur laquelle le rayonnement provenant de la source parasite est réfléchi. La droite Ow fait un angle 8 avec l'axe x'Ox.At the initial instant, the facet plane of reflection is defined by two lines: the axis y'Oy and the line Ow, intersection of the plane xOz with a plane parallel to the facet of the IR dome on which the radiation coming from the spurious source is reflected. The line Ow makes an angle 8 with the axis x'Ox.

Lorsque le missile est animé d'un mouvement de roulis, ce plan facette de réflexion tourne d'un angle α = wt autour de l'axe x'Ox.When the missile is rolled, this facet of reflection turns at an angle α = wt around the axis x'Ox.

La direction du faisceau incident est donnée par la droite OS qui fait dans le plan xOz un angle β avec la facette.The direction of the incident beam is given by the straight line OS which makes an angle β with the facet in the plane xOz.

Dans le système de référence Oxyz,

  • le point générique S du rayon incident OS a pour coordonnées :
    Figure imgb0002
    avec θ = β+ δ et A = OS : paramétre ; →
  • le point générique N de la normale ON au plan de réflexion SN étant perpendiculaire à ON a pour coordonnées :
    Figure imgb0003
    avec B = A (cos δ. sin θ - cos a - sin δ - cos 9) ; →
  • le point générique R du rayon réfléchi OR Intersection de ce rayon avec SN a pour coordonnées :
    Figure imgb0004
    avecxR=A·A·y8=A·A2,zR=A·A3 où A1, A2 et A3 sont des fonctions des lignes trigonométriques de 8, β, et a.
In the Oxyz reference system,
  • the generic point S of the incident ray OS has the coordinates:
    Figure imgb0002
     with θ = β + δ and A = OS : parameter; →
  • the generic point N of the normal ON to the reflection plane SN being perpendicular to ON has the coordinates:
    Figure imgb0003
     with B = A (cos δ. sin θ - cos a - sin δ - cos 9); →
  • the generic point R of the reflected ray OR Intersection of this ray with SN has the coordinates:
    Figure imgb0004
     withx R = A · A · y 8 = A · A 2 , z R = A · A 3 where A 1 , A 2 and A 3 are functions of the trigonometric lines of 8, β, and a.

La figure 4b montre les définitions ci-dessus dans le plan xOz à l'instant initial.Figure 4b shows the above definitions in the xOz plane at the initial time.

Afin de faciliter les calculs, le centre O de référentiel fixe Oxyz est positionné au centre du système optique de l'autodirecteur. Sur la figure 5, ce système optique est représenté d'une manière simplifiée par une lentille 11 située dans le corps du missile 14 attenant à l'IR dôme pyramidal 1. Soit y l'angle de visée c'est-à-dire le débattement de la tête de l'autodirecteur ou dans la représentation simplifiée de la figure, l'angle de l'axe optique de la lentille 11 avec l'axe x'Ox du missile. Co étant le centre du champ dans le plan focal image PF à la distance F du centre O du référentiel, on suppose pour fixer les idées qu'à l'instant initial, l'image se trouve sur l'axe vertical C0Y de symétrie dudit plan, l'axe horizontal C0X étant parallèle à Oy (voir également figure 2). Le plan focal ainsi défini est adressé en coordonnées polaires p, ϕ avec 0≤ p≤ 31 et 0≤ ϕ≤ 127 (p = 0 au centre du champ, p = E[distance au centre P] et ϕ = E[128/2π x angle en radians]) ; dans ces expressions E[x] représente la fonction « arrondi entier de x » et P = 62,5 µm le pas entre deux éléments détecteurs de la barrette.In order to facilitate the calculations, the center O of fixed reference frame Oxyz is positioned at the center of the optical system of the seeker. In FIG. 5, this optical system is represented in a simplified manner by a lens 11 located in the body of the missile 14 adjoining the IR pyramid dome 1. Let y be the angle of sight, that is to say the movement of the seeker head or in the simplified representation of the figure, the angle of the optical axis of the lens 11 with the x'Ox axis of the missile. C o being the center of the field in the image focal plane PF at the distance F from the center O of the frame of reference, it is assumed to fix the ideas that at the initial instant, the image is on the vertical axis C 0 Y of symmetry of said plane, the horizontal axis C 0 X being parallel to Oy (see also Figure 2). The focal plane thus defined is addressed in polar coordinates p, ϕ with 0≤ p≤ 31 and 0≤ ϕ≤ 127 (p = 0 at the center of the field, p = E [distance to the center P] and ϕ = E [128 / 2π x angle in radians]); in these expressions E [x] represents the function "whole rounding of x" and P = 62.5 µm the pitch between two detector elements of the strip.

Les coordonnées de Co dans le référentiel Oxyz sont :

Figure imgb0005
The coordinates of C o in the Oxyz repository are:
Figure imgb0005

L'équation du plan focal PF est donnée par :

Figure imgb0006
The equation of the focal plane PF is given by:
Figure imgb0006

La relation entre le paramètre A qui intervient dans les expressions des coordonnées du point générique refléchi R et la focale F est obtenue en écrivant que R appartient à PF. Cela fournit :

Figure imgb0007
The relation between the parameter A which intervenes in the expressions of the coordinates of the reflected generic point R and the focal length F is obtained by writing that R belongs to PF. This provides:
Figure imgb0007

Dans le référentiel Oxyz de vecteurs de base i, j et k, le vecteur CoR a pour composantes :

Figure imgb0008
In the Oxyz repository of basic vectors i, j and k, the vector C o R has as components:
Figure imgb0008

Dans le plan focal, dont les vecteurs directeurs sont i = j et j = sin γ i + cos γ k, les composantes de CoR sont :

Figure imgb0009
In the focal plane, whose guiding vectors are i = j and j = sin γ i + cos γ k, the components of C o R are:
Figure imgb0009

Ainsi les coordonnées polaires d'une image parasite R dans le plan focal PF s'écrivent :

Figure imgb0010
avec ϕ'R tel que
Figure imgb0011
 Thus the polar coordinates of a parasitic image R in the focal plane PF are written:
Figure imgb0010
 with ϕ ' R such that
Figure imgb0011

La trace d'une trajectoire d'image parasite dans le plan focal est donnée sur la figure 6 avec les valeurs de paramètres :

Figure imgb0012
The trace of a stray image path in the focal plane is given in FIG. 6 with the parameter values:
Figure imgb0012

On voit que l'image parasite située à t = 0 sur l'axe vertical de symétrie du plan focal revient à sa position initiale au bout de 12,5 ms soit 2,5 trames. De t = 0,68 ms à t = 11;82 ms, l'image parasite se trouve hors du champ analysé.We see that the parasitic image located at t = 0 on the vertical axis of symmetry of the focal plane returns to its initial position after 12.5 ms, ie 2.5 frames. From t = 0.68 ms to t = 11; 82 ms, the stray image is outside the analyzed field.

Les trames correspondantes résultent de l'échantillonnage de ces trajectoires par la barrette de détecteurs infrarouge animée d'un mouvement de balayage « type polaire ".The corresponding frames resulting from the sampling of these trajectories by the bar animated infrared detectors of a scanning movement "polar type".

Dans le cas général on ne fait, à priori, aucune hypothèse sur l'existence de l'image parasite à l'instant initial. Le plan focal est défini comme le plan perpendiculaire à l'axe de visée représenté sur la figure 7 et donné par son site γ (compté positivement vers le haut) et son azimut e (compté dans le sens trigonométrique dans le plan horizontal) et tel que le point Co (centre du champ) soit à la distance F de l'origine 0.In the general case, a priori, no assumption is made on the existence of the stray image at the initial instant. The focal plane is defined as the plane perpendicular to the line of sight shown in Figure 7 and given by its site γ (counted positively upwards) and its azimuth e (counted counterclockwise in the horizontal plane) and such that the point C o (center of the field) is at the distance F from the origin 0.

La direction de l'axe de visée est donnée par le vecteur OC0 de composantes :

Figure imgb0013
The direction of the line of sight is given by the vector OC 0 of components:
Figure imgb0013

L'équation du plan focal est alors donnée par :

Figure imgb0014
The equation of the focal plane is then given by:
Figure imgb0014

La relation entre le paramètre A et la focale F obtenue comme précédemment en décrivant que R appartient à PF devient :

Figure imgb0015
The relation between the parameter A and the focal length F obtained as previously by describing that R belongs to PF becomes:
Figure imgb0015

Dans le trièdre Oxyz de vecteurs de base i, j et k, le vecteur CoR a pour composantes :

Figure imgb0016
In the Oxyz trihedron of basic vectors i, j and k, the vector C o R has as components:
Figure imgb0016

Dans le plan focal dont les vecteurs directeurs sont : 1 = - sin E i + cos e j et

Figure imgb0017
les composantes de CoR sont :
Figure imgb0018
 In the focal plane whose direct vectors are: 1 = - sin E i + cos ej and
Figure imgb0017
 the components of C o R are:
Figure imgb0018

Les expressions des coordonnées polaires pR et cpR de l'image parasite R restent celles indiquées ci-dessus.The expressions of the polar coordinates p R and cp R of the parasitic image R remain those indicated above.

Claims (1)

  1. A method of detecting and eliminating parasitic images created by the pyramidal IR dome of an infrared auto-director for a missile which is not roll-stabilised, the method being characterized in that it comprises the formation of an image of a scene delimited by the field of the objective of the auto-director in the focal plane of the said objective after transmission across the dome and the analysis of the said image with a frame scan of period T whose value differs by a multiple of the path period defined as the ratio between the roll rotation period of the missile and the number of facettes of the said dome, said scan being obtained by the analysis of the image in said focal plane of the objective by means of a row of infrared detectors, the image of said scene formed on the row containing, superposed on the useful portion corresponding to said scene delimited by the field of the auto-director, a parasitic image corresponding to a scene located outside sail field and whose flux, transferred across one of the facettes of the dome is reflected from the exterior face of an opposite facette, the method furthermore comprising the storage in a frame memory of electric signals emitted by the said detectors, the levels of the signals corresponding to elements of the frame of the order N-1 preceding any frame of the order N being stored in the said memory, the transfer of the levels of the signals corresponding to two elements of the same geographical localization, one on the frame of order N at an instant t, the other on the frame of order N-1 at the instant t-T, at the non-inverting and at the inverting input, respectively, of a differential detector whose output is connected to a first input of a comparator via an absolute-value calculating device, the comparison of the signal present at the said first input of the comparator to a positive-value threshold voltage applied to the second input of the said comparator, the signal supplied by the said calculating device indicating the appearance of a parasitic image if its value exceeds said threshold value, and to inhibit the taking into account of the said parasitic image by the output signal of the said comparator.
EP85201327A 1984-08-28 1985-08-19 Method for detecting and eliminating parasitic pictures produced by a pyramidal ir dome Expired - Lifetime EP0176121B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8413285A FR2569926B1 (en) 1984-08-28 1984-08-28 DEVICE FOR DETECTING AND ELIMINATING PARASITIC IMAGES CREATED BY A PYRAMIDAL IR DOME
FR8413285 1984-08-28

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EP0176121B1 true EP0176121B1 (en) 1990-02-14

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FR2607917A1 (en) * 1986-12-08 1988-06-10 Roche Kerandraon Oliver SIMPLIFIED INFRARED GUIDANCE FOR ALL PROJECTILES

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US3940767A (en) * 1955-01-21 1976-02-24 Hughes Aircraft Company Electronic radome-error compensation system
US3064924A (en) * 1956-02-27 1962-11-20 North American Aviation Inc Infrared terminal guidance tracking system
GB1005820A (en) * 1958-07-01 1965-09-29 Dehavilland Aircraft Improvements in guided missiles
US3445663A (en) * 1964-06-25 1969-05-20 Hughes Aircraft Co Noise discrimination by unblanking during the time that an a-c reference signal is in the neighborhood of the value it had at the time of the previously accepted pulse
US3535527A (en) * 1968-04-26 1970-10-20 North American Rockwell Digital correlation pattern tracker with single axis scanning
GB1594602A (en) * 1975-06-04 1981-08-05 Marconi Co Ltd Radio systems and apparatus
DE2744985C2 (en) * 1977-10-06 1984-06-07 Messerschmitt-Bölkow-Blohm GmbH, 8012 Ottobrunn Device for eliminating the squint error and the squint error rate of a directional antenna encased by a radome
US4244540A (en) * 1978-09-21 1981-01-13 The United States Of America As Represented By The Secretary Of The Navy Spectral discrimination system for an optical seeker
DE3005427C2 (en) * 1980-02-14 1982-11-04 Messerschmitt-Bölkow-Blohm GmbH, 8000 München All-round tracking system

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US4681282A (en) 1987-07-21
EP0176121A1 (en) 1986-04-02

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